Electrophoresis is the migration of charged electrical species dissolved in an electrolyte solution in response to an applied electric field. Cations (positively charged species) migrate toward the negatively charged cathode and anions (negatively charged species) are attracted toward the positively charged electrode or anode. Capillary electrophoresis (CE) utilizes high voltages across buffer filled capillaries to achieve separation of substances based on the relative charge, and to a smaller extent the size.
The operation of a typical CE system involves the application of a high voltage across capillaries that have been filled with an electrolyte solution that conducts current through the inside of the capillaries. The ends of the capillaries are dipped into reservoirs filled with the electrolyte solution. The reservoirs are usually glass containers that hold a large volume of electrolyte. Electrodes made of an inert material such as platinum are also inserted into the electrolyte reservoirs to complete the electrical circuit. A small volume of a sample is injected into one end of the capillary by applying a voltage across the capillary to induce flow in the buffer solution. The capillary passes through a detector, usually an ultraviolet (UV) absorbance detector, at the end of the capillary that is opposite from the injection end. Application of the voltage once again causes the movement of sample ions in an electroendosmotic flow (EOF) or in a plug-like flow, towards the detection end of the capillary, and allows the separation of positive, neutral, and negatively charged sample ions.
Initial CE systems were bulky, heavy and not easily transported from place to place. These systems required large sample sizes of sometimes expensive substances. Furthermore, a relatively simple, easy method of fabricating these systems does not exist. Therefore, there has been a need to shrink the entire capillary electrophoresis system to a microfabricated microchip capillary system and create a portable analytical instrument (“lab-on-a-chip”).
Attempts at developing integrated CE systems using standard microfabrication techniques have been made. However, these systems have generally included laser-induced florescence detection methods that are implemented with components that are by necessity off-chip and therefore separated from the substrate containing the separation components, and hence not truly integrated.
It is therefore an object of this invention to provide a fully-integrated electrochemical detection system and method for manufacturing such a device.